Method for controlling sulfur concentration in ammonia

ABSTRACT

It is disclosed that the conductivity of a sulfur in ammonia solution is a measure of the sulfur concentration and that sulfur in ammonia solution of predetermined concentration can be continuously prepared by monitoring the conductivity of such solution and controlling at least one feed stream responsive to such monitoring.

United States Patent Appl. No Filed Patented Assignee METHOD FOR CONTROLLING SULFUR [50] Field ofSearch 137/5, 93; 23/ l 15 [56] Reierences Cited UNITED STATES PATENTS 3,438,744 4/ l 969 Steejner l37/5X Primary Examiner-Alan Cohan Attorneys-Joseph C. Kotarski, Henry H. Huth, Jerry B. Peterson, Robert 3 Coleman, Jr. and Carroll Palmer ABSTRACT: It is disclosed that the conductivity of a sulfur in CONFENTRATIPN i AMMONIA ammonia solution is a measure of the sulfur concentration and 3 Clams 4 Drawmg that sulfur in ammonia solution of predetermined concentra- US. Cl 137/5, tion can be continuously prepared by monitoring the conduc- 23/1 15, 137/93 tivity of such solution and controlling at least one feed stream Int. Cl C0lb 17/64 responsive to such monitoring.

SULFUR 28 STORAGE c 200.6

Ev ii. '''i l k 27 400 25 40 ti I. PS? M 34 SULFUR a 23 Li 2 -i 74 60C H 0 (NH4)2 s 0 22 2o PRODUCT zoo- N TO NH; PLANT l4 l9 l3 I7 AIR AIR SEP. 2 SULFUR 50 400C w SCRJBBER BURNER I8 TO WASTE PAIENIEU FEB 2 IEIYI sum 1 0F 2 SULFUR STORAGE 29 60C 200C NH3VAP I 29\ I com). 2?

25 400 E I 400 PSI PSI M 24 SULFUR R NH -H o-s MON'TOR NH4HSO3 NH3 23 L 4 s- H20 7 60C 2 I L (NH4)2 S2 03 3 22 2O PRODUCT 200C N2 TO NH3 PLANT I4 l9 WASH SOLVENT M s /|5 I3 I? 0 AIR AIR SEP. 2 SULFUR 2 400 C SCRJBBER \Ie BURNER lz I TO WASTE I AUDIO Ase OSCILLATOR CELL CONDUCTIVW FROM SULFUR STORAGE i PHASE SENSITIVE DETECTOR VOLTAGE TO CURRENT CONV.

CURRENT TO AIR PRESSURE CONV.

PHASE REFERENCE SIGNAL INVENTORS. RICHARD L. EVERY PAUL F. COX

' ATTORNEY PATENTED FZEB 2:911

SHEET 2 UF 2 0.10 CONDUCTIVITY, MHOS 9 8 7 6 5 4 3 2 l O mahjnm P2mumm P105;

CONDUCTIVITY VS. SULFUR CONCENTRATION INVENTORS. RICHARD L. EVERY BY PAUL F. COX

{I/ 6 gay ATTORNEY METHOD FOR CONTROLLING SULFUR CONCENTRATION IN AMMONIA This is a division of our application having Ser. No. 586,189, filed Oct. l2. I966, for Method for Making Ammonium Thiosulfate and Ammonium Sulfate.- i

This invention relates to a system of control of an ammonium sulfate and thiosulfate process by monitoring unreacted sulfur and controlling the rate of sulfur addition responsive to said monitoring.

It is known to produce ammonium thiosulfate by reacting (NH,).,S with SO in ammonium hydroxide. US. Pat. No. 2, 315,534; by reacting ammonium sulfite andsulfur in aqueous ammonium sulfide, US. Pat. No. 2,4l2,607; and by bubbling through an aqueous ammonia solution of hydrogen sulfide, US. Pat. No. 2,298,l90.Ammonium sulfate is made by oxidizing ammonia and S0,, in the presence of steam or water, US. Pat. No. 1,934,573; and the most important commercial method of making ammonium sulfate is to react concentrated sulfuric acid with an aqueous solution of ammonia.

I All of the above methods involve batch operation; and since the reactions are carried out in solvent mediums, the product to be recovered must be precipitated out either chemically or by crystallization. Another disadvantage of the above methods, is that in orderto obtain the proper ratio of reactants they must be carefully gauged and/or continuous checking of the process by tedious laboratory methods are involved with the consequential delay before a correction can be made.

Thus, it is a primary object of this invention to provide a continuous method of producing the ammonium thiosulfate in a medium wherein the reactants are soluble but the product is insoluble. Another object of the invention is to provide a method of continuously producing thiosulfate wherein the sulfur to the reaction vessel is controlled responsive to theLsulfur concentration in an effluent stream from the reaction vessel.

Another object of this invention is to provide a method of controlling the sulfur content of an ammonia-sulfur solution by continuously measuring conductivity of the solution and regulating at least one feed stream responsive to changes in said conductivity.

In the process, some ammonium sulfate is produced; however, for many applications, this is not harmful and, in fact, is

helpful in many cases. We have found, for example, that the product is useful as a photographic fixing solution, but, more importantly, is an ideal soil conditioner. In the latter application, the product can be added to other fertilizer ingredients or can be applied directly to the soil, preferably by adding the product to an irrigation system.

According to this invention, S0 is reacted with ammonia in aqueous solution to produce ammonium bisulfate, and this product is then reacted with additional ammonia, S0 and sulfur in a strong aqueous ammonia solution to form ammonium thiosulfate which precipitates out as it forms. In one embodiment the sulfur in the effluent from the second reaction is continuously monitored and sulfur addition to the second reaction zone is fed to said zone responsive to said monitoring.

By strong aqueous ammonia, we mean that the water should not be more than about 20 percent, and preferably about percent, of the ammonia and water. This is necessary since the ammonium thiosulfate is soluble in water, whereas our process requires precipitation of product.

The invention can best be described by reference to the drawings of which:

FIG. 1 is a schematic flow sheet for production of ammonium thiosulfate incorporating the method of the invention;

FIG. 2 is a schematic illustration of a typical sulfur monitoring apparatus;

FIG. 3 is a detail of a suitable conductivity cell; and

FIG. 4 is a plot of conductivity of a sulfur in aqueous am monia solution versus percent sulfur.

For convenience, valves, pumps, and the like are not shown; I

it being within the skill of the art to provide these. Details of reaction vessels and/or apparatus construction and shape are also omitted, since these will be of conventional design and well within the skill of them to provide depending uponv desired rates, operating conditions and the like.

In the following description. it is assumed that heat losses will equal heat of reactions; however, this will not be necessarily true in commercial installation The reaction temperatures are not critical. so no particular means for controlling the temperatures and pressures are provided; however, it is within the scope of the invention to provide suitable internal or external cooling means, pressure valves and the like. Preferably. the predetermined reaction temperature will be controlled by the temperature of the feed materials.

Referring now to the drawings and particularly to FIG. I, ammonia and sulfur are passed to vessel I via conduit 2 and at the same time S0 is passed to vessel 1 via conduit 3. The ammonia comes from storage, not shown, whereas sulfur from storage bin 4 passes via conduit 5 to said conduit 2 where it dissolves in the ammonia. The rate of. sulfur flow through conduit 5 is controlled via valve 6 which operates responsive to the sulfur in effluent from vessel I as will hereinafter be described. Also introduced to vessel 1 via conduit 29 are ammonia bisulfite. sulfur and water, from source hereinafter described. Although the temperatures and pressures in vessel 1 are not critical, for thepurpose of this description, we will assume the reaction pressure is 400 p.s.i. and the temperature is C.

The ammonia, sulfur and ammonia bisulfate react to form primarily ammoniumthiosulfate along with lesser amounts of ammonium sulfite and ammonium sulfate. These products are not soluble in the in the ammonia and precipitate out and settle in the vessel. The precipitate can be periodically scaped out via conduit 7, but, preferably, the bottom of this vessel will be cone shaped and the product continuously withdrawn'via said conduit7. It will be obvious that the product will be wet with liquid ammonia, water and dissolved sulfur; and the product can be freed of the ammonia and water by conventional drying means withthe vapors condensed and recycled to the system if desired. In any case, there will also be some sulfur contaminant which can be removed by solvent wash such as NI-I or carbon bisulfide, if desired. However, for fertilizer application, the sulfur contaminant would be a desirable additional ingredient.

There is always an excess of ammonia in vessel I of which'a portion will be vaporized under the reaetion'condition herein" described. These ammonia vapors are taken overhead via conduit. 8 through condenser 9 and the condensed ammonia passed back to vessel-l via conduit 2 with the fresh ammonia TheSO utilized in our method can be supplied from any convenient source. We have chosen to illustrate'combu'stion of sulfur with oxygen; however, it is obvious that air can be used and the S0 separatedfrom'the otheringredients of air composition subsequent to burning.

Air is passed via conduit 10 to zone 11' which'comprises a conventional air separation system, such as--liquefying and scrubbing, to separateO N and CO The'CO and other dissolved contaminants which mightbe present are passed to waste via conduit 12. Wash solventyusually water, is inf troduced to zone 11' via conduit 13.Nitrogen is taken overhead via conduit l4-and sent to storage or ammoniaplant, not shown, as desired.

The oxygen from zone 11 passes to sulfur burner 15 via conduit 16 while sulfur is introduced to the burner via conduit 17.

Thesulfur is burned toSO and leaves the burner at about the nature of a waste heatboilerrhowever, it can be simply a heat exchanger or cooler. The 200 C. SOg'is then divided into two streams,-20 and '21. That S0 in streamor conduit 20 is further cooled in heat exchanger 22 down to theQer nperature of the reactor vessel 1, e.g. 60" C., and passedto vessel 1 via" conduit 3 as previously'described.

The effluent solvent, aqueous ammonia containing sulfur in reaction vessel 1, is passed via conduit 23 to vessel 27. In con-" duit 23,is a sulfur monitoring device 24 which will be hereinafter described with reference to FIG. 2. The amount of sulfur in the effluent is not'critical; however, since" it will show up as impurity in the product. it will generally be held at some percentage less than about 5 percent. preferably 1 to 2 percent. The sulfur content is continuously monitored by the sulfur monitor 24 which is operably connected to control valve 6 via conduit 25. Thus. valve 6 opens and closes thereby controlling the amount of sulfur introduced to vessel 1 responsive to changes detected by means 24. Downstream from monitor 24, water is introduced to conduit 23 via conduit 26. The ammonia, water and sulfur from conduit 23. with additional water from conduit 26, then passes to vessel 27 via conduit 23 wherein it is contacted by SO from conduit 21, previously described. Again. the reaction conditions are not critical however. for the purpose of this description, we will assume 400 psi. and 200 C. The SO then reacts with ammonia and water to form ammonium bisulfite which. along with unreacted water and sulfur, passes via conduit 29 through heat exchanger 28, where the stream is cooled to 60 C back to reaction vessel 1. previously described.

The above process has been described to illustrate the invention. It would be obvious that the sulfur to vessel 1 and the water to vessel 27 could be introduced directly to these vessels, if desired; that an ammonia vapor condenser could be provided for vessel I 27 as is provided for vessel 1; and that bleed valves for removing buildup of undesirable gases and the like can be provided as well as many other modifications as the particular conditions require. In some cases, it might be desirable, for example, to use the effluent cooling water from heat exchangers 22 and 28 for cooling water in heat exchanger 19. This exchanger 19 could be in the form of a waste heat boiler, and the steam used to generate electricity to operate pumps and the like or could be used for driving a steam engine for other power purposes. The use made of this recovered heat or energy is, of course, not a part of this invention.

According to our invention, any method of continuously measuring sulfur concentration in conduit 23 can be employed. The simplest means is by measuring conductivity. Ammonia is similar to water as a solvent. Both have a low conductivity due to autodissociation:

However, both of these solvents have high dielectric constants and support ionization of many solutes. The ions formed increase the solution conductivity. The solubility of sulfur in ammonia is the result of a reaction between sulfur and ammonia in which ammonia and polysulfide ions are formed:

It can be seen then that the conductivity of sulfur-ammonia solutions is many times that of the ammonia alone. A linear within the skill of the art to prepare solutions of known concentrations and to prepare a chart suitable for the selected temperature. Since our description describes a method wherein the temperature of the effluent from vessel 1 is C., this chart was prepared for measuring sulfur concentrations at that temperature and to show that temperature does have an effect by comparing conductivity at two temperatures.

While any means for measuring sulfur concentration and controlling the sulfur feed responsive to changes in the predetermined concentration may be used. FIGS. 2 and 3 illustrates the apparatus utilized by us.

Conductivity cell 30, with inlet 31 and outlet 32 is installed in conduit 23. The cell was made of standard pipe and tubing fittings. The wall of cell, 30 served as one electrode and steel rod 33. insulated from the cell by nylon tubing 34, served as the other electrode. The conductivity cell 30 and variable resistor R with variable capacitor 39 were connected in series with fixed resistors of equal value (R and R to form a bridge. An audio oscillator 36 is connected to the resulting bridge at A and B. The frequency of measurement used by us is 1,000 c.p.s.; however, it will be obvious that other frequencies can be employed, preferably in the range of l00 to l0,000

c.p.s. The variable resistor R is adjusted to the sulfur solutions resistence at the desired concentration and temperature. The variable capacitor 39 compensates for the capacitance of the cell 30. Now, when the resistance across the conductive cell varies, the phase sensitive detector 37 detects the direction and amount of unbalance in the bridge between points C and D. The output voltage from phase sensitive detector 37 is converted to current in current convertor 35, and this current is converted to air pressure in an air pressure converter 38. The air pressure then drives the control valve 6 via conduit 25.

It will be obvious to those skilled in the art that the abovedescribed method of regulating the sulfur content in sulfurammonia solutions would be adaptable to a number of applications. For example, the gas stream containing HZS or SO, passing to an ammonia vessel for reaction to form ammonium thiosulfate and ammonium sulfate with some extra sulfur could be controlled by monitoring the sulfur in the effluent from the reaction vessel. Another example illustrating the use of the method would be to control either the ammonia or the sulfur feed to a mixing zone wherein sulfur and ammonia are .mixed for fertilizer use responsive to monitoring the sulfur content of the effluent from the mixing zone.

It has been proposed to transport sulfur via pipeline by dissolving sulfur in ammonia, the rate of sulfur to the pipeline can be controlled responsive to monitoring the sulfur content of the pipeline. Many other examples of using this method will occur to those skilled in the art.

Several laboratory runs were made using the method of this invention. The product was recovered, washed free of sulfur, dried and analyzed. The results are given in the table.

Reactants, percent Products, percent relationship has been found between sulfur concentration and conductivity (see FIG. 4). In FIG. 4, the conductivity is plotted against concentration measured at 24 C. and 60 C. This conductivity varies with the temperature; however, it is From the table. it can be seen that high yields of the desired ammonium thiosulfate are obtained. All of these products would be useful as fertilizer ingredients and photographic fixing solutions. Particularly the product of Run 2 with a ratio of at least one feedstream upon which 's'aid sulfur content is dependent responsive to changes in said electrical conductivity from a predetermined value 2. The method of claim 1 wherein the rate of addition of sulfur or a sulfur-containing gas is controlled responsive to said changes in electrical conductivity.

3. The method of claim 1 wherein the rate of addition of ammonia is controlled responsive to said changes in electrical conductivity.

H050 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,559, 663 Dated February 2, 1971 InVent1-'(s) Richard T.. Every-Paul l r COJL It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 11, (NH S" should read (NHQ S Column 1, line 15, "2,298, 190" should read 2,898,190 umn 1, line #9, "bisulfate should read bisulfite Cc 2, line 19, "ammonia" should read ammonium Column 2, 2 "ammonia bisulfate" should read ammonium bisulfite Column 3, line 2 1 "vessel 1 27" should read vessel 27 Column l, in the table, last column heading, (NH SO" shoul read (NH SO Column 5, in. ne 1, (N11 20 should 4)2 2 :3

Signed and sealed this 28th day of September 1971 (SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Acting Commissioner of Patent 

2. The method of claim 1 wherein the rate of addition of sulfur or a sulfur-containing gas is controlled responsive to said changes in electrical conductivity.
 3. The method of claim 1 wherein the rate of addition of ammonia is controlled responsive to said changes in electrical conductivity. 